Preparation of polyetherpolyols in the presence of a multimetal cyanide complex catalyst

ABSTRACT

Polyetherpolyols are prepared by reacting diols or polyols with ethylene oxide, propylene oxide, butylene oxide or a mixture thereof in the presence of a multimetal cyanide complex catalyst by a process which is carried out in a vertical, highly cylindrical reactor having a central stirrer and having heat exchanger plates through which a heat-exchange medium flows and which are arranged essentially in the longitudinal direction of the reactor, at an angle α of from 0 to 70° in the direction of rotation of the stirrer relative to the reactor radius.

The present invention relates to a process for the preparation ofpolyetherpolyols.

Polyetherpolyols are provided in large amounts, in particular for thepreparation of polyurethane foams. The known processes for thepreparation of polyetherpolyols are carried out as a rule from alkyleneoxide in the presence of a short-chain initiator with the use ofdifferent catalysts, such as bases, water-repellent double-layerhydroxides, acidic or Lewis acid systems, organometallic compounds ormultimetal cyanide complexes.

Heterogeneous multimetal cyanide complex catalysts are highly selectiveand active catalysts which are suitable in particular for thepreparation of flexible-foam polyetherpolyols, where a high molecularweight has to be reached and long oxyalkylation times are required. Byusing multimetal cyanide complex catalysts, the production costs can bereduced and at the same time high-quality polyetherpolyol which can befurther processed to give polyurethane foams which have little odor andare therefore of high quality can be obtained. The literature disclosesthat secondary reactions which can lead to the formation of odoroussubstances and unsaturated components scarcely occur.

However, the high activity has the result that the heat of reaction canno longer be removed in conventional reactors. If the polyetherpolyolpreparation catalyzed by a multimetal cyanide complex is carried out instandard stirred kettles, the metering rates of alkylene oxide arelimited by the heat removal rate of the heat exchanger.

U.S. Pat. No. 5,811,595 proposes an ideally mixed reactor comprising oneor two heat exchangers, the polyetherpolyol being fed into thecirculation stream of the heat exchanger and the ethylene oxide into thereactor. Mixing of the ethylene oxide with the liquid phase is achievedby means of a nozzle.

Disadvantages of this process are the high circulation rate required formaintaining the high heat removal rate and the danger of mechanicaldamage to the heterogeneous catalyst by the pump. Moreover, the highlyreactive ethylene oxide is introduced into the reactor in which, owingto the cooling collars used, the heat removal is very poor, inparticular at low fill levels, because of the small exchange area.Overheating owing to the high reaction rate, resulting in damage to theproduct, can occur. This may be increased by the poor mixing in thereactor.

EP-A-0 850 954 describes a process in which the reaction takes place inthe gas space above the reaction liquid. The polyetherpolyol iscirculated via a heat exchanger and fed in through nozzles. This resultsin a large liquid surface. Simultaneously with this, ethylene oxide andpolyetherpolyols are metered in via nozzles. The large surface resultsin good mass transfer and hence high reaction rates.

Owing to the high reaction rate which can be achieved with this process,local excess temperatures are likely in the individual droplets and inturn may result in damage to the product. Furthermore, here too the highcirculation rate required for heat removal is not without problems forthe heterogeneously dispersed multimetal cyanide complex catalyst; thedanger of damage cannot be ruled out.

The artificially enlarged gas phase is a further potential danger, inparticular in the ethoxylation, since free alkylene oxide is present inthe gas phase. Ethylene oxide tends to gas-phase decomposition, whichcan lead to bursting of the reactor. On the other hand, when thepolyetherpolyol or ethylene oxide is passed into the liquid, rapidreaction of the alkylene oxide is to be expected owing to the activemultimetal cyanide complex.

EP-B-0 633 060 discloses a reactor for gas-liquid reactions whichcomprises a central stirring apparatus, around which heat exchangerplates through which a heat-exchange medium flows are arranged at anangle from 0 to 70° in the direction of rotation of the stirrer relativeto the reactor radius. As a result of the direct heat removal at thepoint of heat generation, higher productivity, a high product qualityand reduced catalyst consumption can be ensured. The reactor EP-B-0 633060 was proposed in particular for highly exothermic catalytichydrogenation reactions.

It is an object of the present invention to provide a process whichemploys a simple apparatus for the preparation of polyetherpolyols inthe presence of multimetal cyanide complex catalysts with improvement ofthe space-time yield and avoidance of local overheating and hence ahigher level of secondary reactions, thus ensuring a high productquality.

We have found that this object is achieved by a process for thepreparation of polyetherpolyols by reacting diols or polyols withethylene oxide, propylene oxide, butylene oxide or a mixture thereof inthe presence of a multimetal cyanide complex catalyst.

In the invention, the reaction is carried out in a vertical, highlycylindrical reactor having a central stirrer and having heat exchangerplates through which a heat-exchange medium flows and which are arrangedessentially in the longitudinal direction of the reactor, at an angle αof from 0 to 70° in the direction of rotation of the stirrer relative tothe reactor radius.

The vertical, highly cylindrical reactor described in EP-B-0 633 060 andhaving a central stirrer and having heat exchanger plates through whicha heat-exchange medium flows and which are arranged essentially in thelongitudinal direction of the reactor, at an angle of α of from 0 to 70°in the direction of rotation of the stirrer relative to the reactorradius was developed in particular for highly exothermic catalytichydrogenation reactions. These involve low-viscosity liquid reactionmixtures, i.e. liquids which have a viscosity substantially below 10mPa.s under reaction conditions.

In contrast, the inventors of the present process have surprisinglyfound that the reactor type disclosed in EP-B-0 633 060 can also be usedfor reaction media having a higher viscosity, such as thepolyetherpolyols of the present invention. As a rule, polyetherpolyolshave high viscosities, about in the range from 80 to 1000 mPa.s at roomtemperature and still above 20 mPa.s, frequently above 100 mPa.s, underreaction conditions (from about 100 to 130° C.). It is known that theboundary layer between heat exchanger and reaction mixture increaseswith increasing viscosity, with the result that the heat is increasinglypoorly removed. According to the novel process, sufficient heat removalcould be achieved in spite of the increased viscosity, so that highalkylene oxide metering rates could be realized, resulting in animproved space-time yield and hence higher productivity and a goodproduct quality. Local excess temperatures which might lead to damage tothe product were avoided.

According to the invention, diols or polyols are initially takentogether with a multimetal cyanide complex catalyst in a vertical,highly cylindrical reactor having a central stirrer and having heatexchanger plates through which a heat-exchange medium flows and whichare arranged essentially in the longitudinal direction of the reactor,at an angle α of from 0 to 70° C. in the direction of rotation of thestirrer relative to the reactor radius, and are then reacted withethylene oxide, propylene oxide, butylene oxide or a mixture thereof.After the alkylene oxide has completely reacted, the reaction product isremoved from the reactor.

The invention does not include any restrictions with regard to themultimetal cyanide complex catalyst which may be used; it may have anamorphous form but preferably has an at least partially, predominantlyor completely crystalline form. If required, the catalyst is supported.Particularly preferably used multimetal cyanide complex catalysts arethose of the formula (I)M¹ _(a)[M²(CN)_(b)L¹ _(c)]_(d)·e(M¹ _(f)X_(g))·hL².iH₂O  (I)

-   -   where M¹ is at least one element from the group consisting of        Zn(II), Fe(II), Co(III), Ni(II), Mn(II), Co(II), Sn(II), Pb(II),        Fe(III), Mo(IV), Mo(VI), Al(III), V(IV), V(V), Sr(II), W(IV),        W(VI), Cu(II), Cd(II), Hg(II), Pd(II), Pt(II), V(III), Mg(II),        Ca(II), Sr(II), Ba(II) and Cr(III),    -   M² is at least one element from the group consisting of Fe(II),        Fe(III), Co(III), Cr(III), Mn(II), Mn(III), Ir(III), Rh(III),        Ru(II), V(IV), V(V), Co(II) and Cr(II),    -   L¹ is at least one ligand from the group consisting of cyanide,        carbonyl, cyanate, isocyanate, nitrile, thiocyanate and        nitrosyl,    -   X is a formate anion, acetate anion or propionate anion,    -   L² is at least one water-miscible ligand from the group        consisting of alcohols, aldehydes, ketones, ethers, polyethers,        esters, urea derivatives, amides, nitriles and sulfides,    -   a, b, d, e, f and g are integers or fractions greater than zero,    -   c, h and i are integers or fractions greater than or equal to        zero,    -   a, b, c and d being chosen so that the electroneutrality        condition is fulfilled and    -   f and g being chosen so that the electroneutrality condition is        fulfilled, whose X-ray diffraction pattern has reflections at at        least the d values    -   6.10 Å±0.004 Å    -   5.17 Å±0.04 Å    -   4.27 Å±0.02 Å    -   3.78 Å±0.02 Å    -   3.56 Å±0.02 Å    -   3.004 Å±0.007 Å    -   2.590 Å±0.006 Å    -   2.354 Å±0.004 Å    -   2.263 Å±0.004 Å    -   if X is a formate anion, whose X-ray diffraction pattern has        reflections at at least the d values    -   5.20 Å±0.02 Å    -   4.80 Å±0.02 Å    -   3.75 Å±0.02 Å    -   3.60 Å±0.02 Å    -   3.46 Å±0.01 Å    -   2.824 Å±0.008 Å    -   2.769 Å±0.008 Å    -   2.608 Å±0.007 Å    -   2.398 Å±0.006 Å    -   if X is an acetate anion, and whose X-ray diffraction pattern        has reflections at at least the d values    -   5.59 Å±0.05 Å    -   5.40 Å±0.04 Å    -   4.08 Å±0.02 Å    -   3.94 Å±0.02 Å    -   3.76 Å±0.02 Å    -   3.355 Å±0.008 Å    -   3.009 Å±0.007 Å    -   2.704 Å±0.006 Å    -   2.381 Å±0.004 Å    -   if X is a proprionate anion or which have a monoclinic crystal        system if X is an acetate anion.

Such multimetal cyanide complex catalysts are described in DE-A-197 42978.

According to the invention, the process is carried out in a vertical,highly cylindrical reactor having a central stirrer and having heatexchanger plates through which a heat-exchange medium flows and whichare arranged essentially in the longitudinal direction of the reactor,at an angle α of from 0 to 70° in the direction of rotation of thestirrer relative to the reactor radius. Such a reactor is described inEP-B-0 633 060, preferably for highly exothermic hydrogenationreactions.

The multimetal cyanide complex catalyst is preferably used in amounts ofless than 250 ppm, particularly preferably less than 100 ppm, inparticular less than 50 ppm, based on the mass of product to beproduced. In reactors equipped with heat exchanger plates, there is thedanger that heterogeneous catalysts would be deposited in corners,angles or other areas with insufficient flow and will consequently beavailable only in an insufficient amount, if at all, for the catalyticreaction. This problem is not so critical at relatively high catalystconcentrations because a catalyst loss in this case does not have anyextreme effect on the quality of the catalysis and of the products. Onthe other hand, at low catalyst concentrations, for example 100 ppm orless, the loss of available catalyst, even in an order of magnitude of afew 10 ppm, means a dramatic absolute loss of catalyst material andhence of catalyst activity. The result is substantially poorer productquality, broader molecular weight distributions and high molecularweight fractions. In contrast, it was surprisingly found that, in thenovel process, such problems, did not occur in spite of very lowcatalyst concentrations and the high viscosity of the polyol, and nodeterioration in the product quality took place.

In a preferred embodiment, the heat exchanger plates are bent or curvedin the direction of rotation of the stirrer. This reduces the mechanicalresistance.

A preferably used heat-exchange medium is water.

According to a preferred embodiment, the heat-exchange medium is passedfrom the heat exchanger plates in a loop flow via a heat exchangerarranged outside the reactor. Consequently, the heat removal can beadditionally improved.

In order to ensure heat removal in the case of small amounts ofinitiator and to permit heating-up of the initiator, in particular atthe beginning of the reaction, a further heat exchanger may also bearranged on the outer jacket of the reactor.

The heat exchanger arranged on the outer jacket of the reactor ispreferably in the form of heat exchanger half-tubes.

The reaction is preferably carried out at from 90 to 200° C. and from 1to 50 bar.

A temperature range of from 110 to 140° C. and a pressure of from 2 to10 bar are particularly preferred.

The reaction is preferably carried out by the semibatch procedure, i.e.initiator and catalyst are initially taken and the alkylene oxide, i.e.ethylene oxide, propylene oxide, butylene oxide or a mixture thereof, ismetered into the reactor until the desired molar mass is reached. Thisensures that, on the one hand, there is no accumulation of alkyleneoxide and hence the danger of a runaway reaction is avoided and, on theother hand, safe temperature control is achieved. Thus, exact control ofthe residence time required for constant molecular weight distributioncan be achieved.

By introducing stirring energy via the central stirrer, thorough mixingof all components of the reaction mixture is achieved. The arrangementof the heat exchanger plates in the reactor at an angle α of from 0 to70° in the direction of rotation of the stirrer relative to the reactorradius leads to virtually complete freedom from a reaction temperaturegradient over the reactor. Consequently, local overheating is avoided,resulting in a substantial suppression of secondary reactions andsubstantial avoidance of catalyst deactivation. Accordingly, highspace-time yields are achieved, which are attributable to the good heatremoval and the high alkylene oxide metering rate thus possible.

The invention is explained in more detail below with reference to anembodiment:

The following methods of determination were used:

The content of unsaturated components was determined via the iodinenumber. For this purpose, in a first process, the unsaturated fractionswere brominated and excess bromine was reacted with potassium iodidesolution with precipitation of iodine. The content of unsaturatedcomponents in milliequivalents/g (meq/g) was obtained by titrating theprecipitated iodine with thiosulfate solution. The cycloacetal contentwas determined by headspace GC-MS analysis, the mass trace of m/e=130being monitored. The sample temperature was 130° C.

COMPARATIVE EXAMPLE

An initiator (glyceryl propoxylate) having an average molar mass of 400g/mol was initially taken in a stirred kettle having internal coolingcoils. 100 ppm, based on the final polyol mass, of DMC were added.

The preparation of the multimetal cyanide catalyst was carried out in atwo-stage process, in which first the acid and then the catalyst wasobtained by precipitation. For this purpose, 7 l of strongly acidic ionexchanger which was in the sodium form, i.e. Amberlite® 252 Na from Rohm& Haas, were filled into an exchanger column having a length of 1 m anda volume of 7.7.l The ion exchanger was then converted into the acidform by passing 10% strength hydrochloric acid at a rate of 2 bedvolumes per hour over the exchanger column for 9 hours until the sodiumcontent in the discharge was <1 ppm. The ion exchanger was then washedwith water. The regenerated ion exchanger was then used for preparing anessentially alkali-free hexacyanocobaltic acid. For this purpose, a 0.24molar solution of potassium hexacyanocobaltate in water was passed overthe ion exchanger at a rate of one bed volume per hour. After 2.5 bedvolumes, the potassium hexacyanocobaltate solution was replaced withwater. The 2.5 bed volumes obtained had on average a content of 4.5% byweight of hexacyanocobaltic acid and alkali contents of <1 ppm.

For the preparation of the catalyst, 8553.5 g of zinc acetate solution(content of zinc acetate dihydrate: 8.2% by weight, content of Pluronic®PE 6200, i.e. a block copolymer of ethylene oxide and propylene oxide,which is used for controlling the crystal morphology: 1.3% by weight)were then initially taken in a 20 l reactor and heated to 60° C. whilestirring. 9956 g of hexacyanocobaltic acid solution (cobalt content 9g/l, content of Pluronic® PE 6200 1.3% by weight) was then added in thecourse of 20 minutes at 60° C. with constant stirring. The suspensionobtained was stirred for a further 60 minutes at 60° C. Thereafter, thesolid thus obtained was filtered off and was washed with 6 times thecake volume. The moist filter cake was then dispersed in polypropyleneglycol having a molar mass of 400 g/mol.

The dispersion thus obtained was used as the catalyst.

Dewatering was carried out for 1 hour under reduced pressure, afterwhich propoxylation was effected until a molar mass of 3000 g/mol wasreached. A space-time yield of 210 kg/m³/h was obtained from the feedrate of the propylene oxide, which was limited only by the heat removalrate. A content of unsaturated components of 0.0052 meq/g was found. Thecontent of cycloacetals was 0.06 ppm.

EXAMPLE

The reaction was carried out under the same experimental conditions asin the Comparative Example, but in a cylindrical reactor having acentral stirrer with heat exchanger plates through which water flows andwhich were arranged in the longitudinal direction of the reactor andradially in the reactor. The reactor had a capacity of 40 t and theheat-exchange area was 600 m². As a result of the improved heat removal,the feed rate of the propylene oxide could be increased by a factor of1.8 and consequently the space-time yield could be increased to 380kg/m³/h. The contents of unsaturated components and cycloacetals weredetermined as 0.0050 meq/g and 0.04 ppm, respectively.

Thus, by using the novel reactor, it was possible to achieve an increaseof 80% in the space-time yield with slightly improved product quality.

1. A process for the preparation of polyetherpolyols comprising reactinga reaction mixture comprising diols or polyols, ethylene oxide,propylene oxide, butylene oxide or a mixture thereof, andpolyetherpolyols in the presence of a multimetal cyanide complexcatalyst, wherein the reaction is carried out in a vertical, highlycylindrical reactor having a central stirrer and having heat exchangerplates through which a heat-exchange medium flows and which are arrangedessentially in the longitudinal direction of the reactor, at an angle offrom 0 to 70° in the direction of rotation of the stirrer relative tothe reactor radius, and wherein the polyetherpolyols in the reactionmixture have a viscosity of greater than 20 mPa.s at a temperature offrom 100 to 130° C.
 2. A process as claimed in claim 1, wherein the heatexchanger plates are arranged radially.
 3. A process as claimed in claim1, wherein the multimetal cyanide complex catalyst is used in aconcentration of less than 250 ppm, based on the mass of product to beproduced.
 4. A process as claimed in claim 1, wherein the heat exchangerplates are bent or curved in the direction of rotation of the stirrer.5. A process as claimed in claim 1, wherein the heat-exchange medium ispassed from the heat exchanger plates in a loop flow via a heatexchanger arranged outside the reactor.
 6. A process as claimed in claim1, wherein a heat exchanger is arranged on the outer jacket of thereactor.
 7. A process as claimed in claim 6, wherein the heat exchangerarranged on the outer jacket of the reactor is in the form of heatexchanger half-tubes.
 8. A process as claimed in claim 1, wherein thereaction is carried out at from 90 to 200° C. and from 1 to 50 bar.
 9. Aprocess as claimed in claim 8, wherein the reaction is carried out atfrom 110 to 140° C. and from 2 to 10 bar.
 10. A process as claimed inclaim 1, wherein the multimetal cyanide complex catalyst corresponds tothe formula (I)M¹ _(a)[M²(CN)_(b)L¹ _(c)]d e(M¹ _(f)X_(g))hL².iH₂O  (I) where M¹ is atleast one element from the group consisting of ZN(II), Fe(ll), Co(III),Ni(II), Mn(II), Co(II), Sn(II), Pb(II), Fe(III), Mo(IV), Mo(VI),Al(III), V(IV), V(V), Sr(II), W(VI), Cu(II), Cd(II), Hg(II), Pd(II),Pt(II), V(III), Mg(II), Ca(II), Sr(II), Ba(II) and Cr(III), M² is atleast one element from the group consisting of Fe(II), Fe(III), Co(III),Cr(III), Mn(II), Mn(III), Ir(III), Rh(III), Ru(II), V(IV), V(V), Co(II)and Cr(II), L¹ is at least one ligand from the group consisting ofcyanide, carbonyl, cyanate, isocyanate, nitrile, thiocyanate andnitrosyl, X is a formate anion, acetate anion or propionate anion, L² isat least one water-miscible ligand from the group consisting ofalcohols, adehydes, ketones, ethers, polyethers, esters, ureaderivatives, amides, nitriles and sulfides, a, b, c, d, e, f, g, h and iare integers, a, b, c and d being chosen so that the electroneutralitycondition is fulfilled and f and g being chosen so that theelectroneutrality is fulfilled, whose X-ray diffraction pattern hasreflections at at least the d values 6.10 Å±0.004 Å 5.17 Å±0.04 Å 4.27Å±0.02 Å 3.78 Å±0.02 Å 3.56 Å±0.02 Å 3.004 Å±0.007 Å 2.590 Å±0.006 Å2.354 Å±0.004 Å 2.263 Å±0.004 Å if X is a formate anion, whose X-raydiffraction patter has reflections at at least the d values 5.20 Å±0.02Å 4.80 Å±0.02 Å 3.75 Å±0.02 Å 3.60 Å±0.02 Å 3.46 Å±0.01 Å 2.824 Å±0.008Å 2.769 Å±0.008 Å 2.608 Å±0.007 Å 2.398 Å±0.006 Å if X is an acetateanion, and whose X-ray diffraction pattern has reflections at at leastthe d values 5.59 Å±0.05 Å 5.40 Å±0.04 Å 4.08 Å±0.02 Å 3.94 Å±0.02 Å3.76 Å±0.02 Å 3.355 Å±0.008 Å 3.009 Å±0.007 Å 2.704 Å±0.006 Å 2.381Å±0.004 Å if X is a proprionate anion or which have a monoclinic crystalsystem if X is an acetate anion.
 11. A process as claimed in claim 1,wherein the multimetal cyanide complex catalyst is substantially orcompletely crystalline.
 12. A process as claimed in claim 11, wherein amultimetal cyanide complex catalyst of the zinc-cobalt type is used. 13.A process as claimed in claim 1, wherein the multimetal cyanide complexcatalyst is used in a concentration of less than 100 ppm, based on themass of product to be produced.
 14. A process as claimed in claim 1,wherein the multimetal cyanide complex catalyst is used in aconcentration of less than 50 ppm, based on the mass of product to beproduced.
 15. A process as claimed in claim 1, wherein the polyetherolsin the reaction mixture have a viscosity of greater than 100 mPa.s. 16.A process as claimed in claim 1, wherein the polyetherols in thereaction mixture have a viscosity of from 80 to 1000 mPa.s.